High transduction (HT) mutants of P22 bacteriophage will be examined to ascertain if particles contain a unique protein and if abortively transduced DNA molecules are circularized in a protein complex, as found for Pl phage. If circular molecules are found in recipient bacteria, the origin of the protein "linker" will be ascertained. Regulation of the histidine operon in Salmonella typhimurium will be studied in vitro in an attempt to isolate and characterize a histidine-specific regulatory factor. The histidine biosynthetic enzymes and histidyl-tRNA synthetase will be studied through the use of cross-linking agents to determine if an oligomeric complex exists in vivo and if such a complex, in fact, is intimately involved in histidine-specific regulation of transcription. Reaction products of nitrous acid action on polyamines will be further characterized with regard to their nature and proficiencies in mutagenesis. The possible involvement of Exonuclease I in mutation-prone DNA repair will be examined in Escherichia coli. Finally, possible microbial associations and antagonisms on man will be assessed through computer-assisted "cluster analysis" on tens of thousands of patient specimens and laboratory tests on selected culture samples.